This invention relates to a process chamber for processing a substrate in a process gas.
In semiconductor fabrication processes, process gas is introduced into a process chamber through a gas distributor, optionally, a plasma is formed from the gas to etch features on the substrate or deposit layers of material on the substrate, and gaseous byproducts are exhausted from the process chamber via an exhaust system. In etching processes, the uniformity of the shape and size of features across the substrate is affected by the distribution of gaseous species across the substrate, especially when the size and spacings of the etched features become smaller. Similarly, in deposition processes, the thickness and composition of the deposited layer can vary across the surface of the substrate depending upon the distribution of gaseous species across the surface of the substrate.
Conventional process chambers, gas distributors, and exhaust systems often fail to provide a uniform distribution of reactive gaseous species across the substrate resulting in variations in the shape of the etched features or the thickness of the deposited layer. Shower-head gas distributors that inject process gas directly above the substrate can provide an asymmetric distribution of process gas across the substrate because higher gas flow rates occur over central portions of the substrate and lower flow rates at peripheral portions. Conversely, gas distributors that inject process gas from around the peripheral edge of the substrate provide higher concentrations of gas at the peripheral edge of the substrate. The distribution of gas in the chamber is also affected by the position and symmetry of the exhaust conduit of the process chamber. Asymmetrically positioned exhaust conduits result in asymmetric flow rates of gas across the substrate. Furthermore, as substrates increase in diameter up to 300 mm and beyond, the corresponding increases in the volume of the process chamber makes it even more difficult to provide a uniform distribution of process gas across the entire surface of the substrate.
The distribution of gas across the substrate can be improved by supplying the gas through a plurality of nozzles that extend through the ceiling or walls of the process chamber. However, chambers having ceramic walls or ceilings are difficult to fabricate with nozzle feedthroughs extending therethrough. The ceramic walls of polycrystalline ceramic material, such as aluminum oxide or silicon, are brittle materials and it is difficult to machine holes for passing feedthroughs through these materials without breaking or otherwise damaging the ceramic. Also, other components, such as RF induction coils, which are located adjacent to the ceramic walls further reduce the available space for locating a gas nozzle through the ceramic walls. Thus, there is a need for a process chamber having a gas distributor that provides a uniform distribution of gas in the process chamber without requiring an excessive number of feedthroughs to be machined through chamber walls.
Another problem with conventional process chambers arises because the gas distributors have fixed locations within the chamber which cannot be easily changed or adapted for different processes. For example, in one chamber design, gas nozzles extend through sidewalls and terminate near the edge of the substrate. The gas nozzles cannot be easily moved from one location to another in the process chamber without drilling additional holes in the chamber walls and sealing off the old holes. In addition, the gas nozzles have outlets with fixed sized diameters. However, new fabrication processes often require different introduction points and different flow rates of gas into the chamber. For example, as the gas flow rates into the chamber increase for larger diameter substrates, the desired gas introduction points also change. Thus, it is desirable to have a process chamber with a gas distributor that is adaptable to change the point source or flow rate of gas introduced into the chamber.
A further problem arises when a portion of the gas distributor is made from metal and is located within the energized plasma sheath in the process chamber. The metal component causes localized energy perturbations that lead to variations in plasma energy across the face of the substrate. In addition, the plasma species often chemically erode the metal to form contaminant particles that deposit upon the substrate. For example, an aluminum gas distributor is rapidly eroded by a halogen containing plasma. Thus, it is desirable for the metal portion of the gas distributor to be protected from erosion and electrically isolated from the plasma provide a more uniform plasma distribution.
Therefore, there is a need for a process chamber having a gas distributor capable of providing a uniform distribution of gas in the process chamber, especially for process chambers having ceramic walls or ceilings. There is also a need for a gas distributor that can be adapted to vary the distribution pattern or point sources of gas being introduced into the process chamber, which is determined by the location of the gas sources in the process chamber and the gas flow rates. In addition, there is a need for a gas distributor that is resistant to erosion by the plasma environment and that can be easily electrically isolated from the plasma.